The present invention relates to an absorbent article, such as a diaper, a pants-type diaper, an incontinence protector or a pants-like sanitary napkin, said article including a front part, a rear part and an intermediate central part and also including an absorbent body which is enclosed between a liquid-permeable inner sheet or top sheet and a liquid-impermeable outer sheet or backing sheet, and fastener devices by means of which the side-portions of the front and rear parts can be releasably fastened together either directly or indirectly. The fastener devices are located on the same side of the longitudinal symmetry line of said article and are produced from a renewable material.
The use of fastener devices that include mechanically coacting elements is becoming more and more popular. Manufacturers are beginning to give absorbent articles a pants-like configuration. Many requirements are placed on mechanically coacting elements of this nature. Among other things, they should be easy to open and close and soft enough to ensure that a baby or other person wearing said article will not be injured by the fastener elements. They must also be made of relatively inexpensive material because of the one-time use nature of the products to which they are attached. Such fastener devices are often made of plastic material, such as polypropylene for instance, and represent a not-insignificant percentage of the material consumed in article manufacture when seen as a whole. It is well known that the oil from which the raw material for plastic materials derives is not a renewable resource and the use of plastic materials draws on the earth""s natural oil resources. It is known from EP-A2-0 809 952 to manufacture fastener devices from a water-soluble or biologically degradable resin, wherewith the fastener device has an underside which becomes adhesive upon contact with water. Polylactic acid is mentioned as one possible material from which these fastener devices can be made.
Since the use of gluing as a joining method has the drawbacks of incurring high material costs and production complications incurred by waste and delays in the process line, it is preferred to weld the fastener devices to the side-portions of the products. Plastic material is thermally welded or ultrasonically welded to the outer sheets and backing sheets normally used in the aforesaid products. However, a relatively large amount of energy is consumed in producing weld joins of sufficient strength between outer sheets and plastic fastener devices by heat welding or ultrasonic welding processes. The maximum welding speed, i.e. the highest speed, at which a web of material can be moved past a welding unit while producing weld joins of sufficient strength constitutes a limiting parameter with respect to the number of products of the aforesaid kind that can be produced per unit of time in a continuous article manufacturing line. There is thus a need to reduce the amount of energy consumed in fastening such fastener devices, so as to achieve the advantage of enabling higher welding speeds to be used in addition to saving energy.
The object of the present invention is to satisfy these needs and to enable the fastener devices to be made from renewable material.
These objects are achieved in accordance with the invention with an absorbent article, such as a diaper, a pants-like diaper, an incontinence protector or a pants-like sanitary napkin, of the aforesaid kind, wherein said article is characterised in that the fastener devices are welded to at least one of the outer sheets of said article; and in that the outer sheet or sheets to which said fastener devices is/are fastened is/are made of a material that has a glass transition temperature that lies between 50-60xc2x0 C. and a melting point or melting point that lies between 140-180xc2x0 C., preferably between 150-175xc2x0 C.
In one preferred embodiment, the fastener devices and the outer sheet or sheets to which said devices is/are fastened is/are produced mainly or entirely from polylactic acid. The fastener devices each include two mutually coacting elements of which one element is fastened to the front side-portion of the article and the other element is fastened to the rear side-portion of said article and said coacting elements are fastened to either the same or to different outer sheets of said article. When the coacting elements are fastened to different outer sheets, both of said sheets are made of a material that has a glass transition temperature which lies between 50-60xc2x0 C. and a melting temperature which lies between 140-180xc2x0 C., preferably between 150-175xc2x0 C.
The fastener devices may be made of polylactic acid, a lactic acid copolymer that includes caprolactone for instance, plasticized or softened polylactic acid or a laminate (coextrudate) that consists of a combination of these materials.
In a first variant, the fastener devices include two mechanically coacting fastener elements of which one element includes a part which projects out from the plane of said element and which can be inserted into a recess or aperture of corresponding form in the other element, the direction of insertion being parallel to the plane of said elements. The fastener elements are fastened to the liquid-impervious outer sheet.
In another variant, each of the fastener devices includes two mechanically coacting fastener elements which each include hooked parts that have a mutually complementary form. The fastener elements of this variant are fastened to different outer sheets.
In a third variant, each of the fastener devices includes two mechanically coacting fastener elements that include parts which can be snapped into each other.
In a fourth variant, the fastener devices each include two mechanically coacting fastener elements which include hook and loop members.
In a fifth variant, the fastener devices each include an adhesive tab.